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APPENDIX Equation (4) must be changed to accommodate Hillert's analysis. Instead of normalizing D with respect to D, 9/86 (the critical grain size) is used; and a new parameter u = 8/9(D/D) is defined as the relative grain size. Making these alterations to Eq. (4), P U " ,

The oxidation of 304L stainless steel has been measured in steam and in air in the temperature range from 1000 to 1375 C (1832 to 2507 F) using a thermogravimetric technique. This temperature range is of interest in the analysis of a reactor loss-of-coolant accident. Experiments in steam showed initial linear weight gain with time for the first 6 to 28 minutes, followed by parabolic rate behavior. The linear reaction rate constant W/t was found to be 1.1 × 105 exp (−44,350/RT) while the parabolic constant W2/t was found to be 2.4 × 101 2 exp (−84,300/RT), where T is in °K and W is in mg/cm2 and t is in sec. The parabolic rate controlling process is diffusion through an Fe-Ni-Cr spinel layer observed in the inner layer of the scale. The oxidation of 304L stainless steel by air from 1100 to 1360 C (2012 to 2480 F) was slow compared to the oxidation by steam in this same temperature range, parabolic rates being lower than those in steam by a factor of ~ 103. Although X-ray diffraction observed Fe3O4 (major) and Fe2O3 (minor) on the surface of the coatings formed in air at temperatures of 1360 C and below, Cr2O3 was found at the metal-oxide interface. The low rates in air thus reflect the formation of a protective Cr2O3 film. The rate in air at 1375 C is exceptionally rapid compared to those at the lower temperatures possibly because of the Fe-FeO liquidus at 1370 C (2498 F).